src/runtime/testdata/testprog/gc.go - go - Git at Google

 // Copyright 2015 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package main

 import (
 	"fmt"
 	"os"
 	"runtime"
 	"runtime/debug"
 	"sync/atomic"
 	"time"
 )

 func init() {
 	register("GCFairness", GCFairness)
 	register("GCFairness2", GCFairness2)
 	register("GCSys", GCSys)
 	register("GCPhys", GCPhys)
 	register("DeferLiveness", DeferLiveness)
 }

 func GCSys() {
 	runtime.GOMAXPROCS(1)
 	memstats := new(runtime.MemStats)
 	runtime.GC()
 	runtime.ReadMemStats(memstats)
 	sys := memstats.Sys

 	runtime.MemProfileRate = 0 // disable profiler

 	itercount := 100000
 	for i := 0; i < itercount; i++ {
 		workthegc()
 	}

 	// Should only be using a few MB.
 	// We allocated 100 MB or (if not short) 1 GB.
 	runtime.ReadMemStats(memstats)
 	if sys > memstats.Sys {
 		sys = 0
 	} else {
 		sys = memstats.Sys - sys
 	}
 	if sys > 16<<20 {
 		fmt.Printf("using too much memory: %d bytes\n", sys)
 		return
 	}
 	fmt.Printf("OK\n")
 }

 var sink []byte

 func workthegc() []byte {
 	sink = make([]byte, 1029)
 	return sink
 }

 func GCFairness() {
 	runtime.GOMAXPROCS(1)
 	f, err := os.Open("/dev/null")
 	if os.IsNotExist(err) {
 		// This test tests what it is intended to test only if writes are fast.
 		// If there is no /dev/null, we just don't execute the test.
 		fmt.Println("OK")
 		return
 	}
 	if err != nil {
 		fmt.Println(err)
 		os.Exit(1)
 	}
 	for i := 0; i < 2; i++ {
 		go func() {
 			for {
 				f.Write([]byte("."))
 			}
 		}()
 	}
 	time.Sleep(10 * time.Millisecond)
 	fmt.Println("OK")
 }

 func GCFairness2() {
 	// Make sure user code can't exploit the GC's high priority
 	// scheduling to make scheduling of user code unfair. See
 	// issue #15706.
 	runtime.GOMAXPROCS(1)
 	debug.SetGCPercent(1)
 	var count [3]int64
 	var sink [3]interface{}
 	for i := range count {
 		go func(i int) {
 			for {
 				sink[i] = make([]byte, 1024)
 				atomic.AddInt64(&count[i], 1)
 			}
 		}(i)
 	}
 	// Note: If the unfairness is really bad, it may not even get
 	// past the sleep.
 	//
 	// If the scheduling rules change, this may not be enough time
 	// to let all goroutines run, but for now we cycle through
 	// them rapidly.
 	//
 	// OpenBSD's scheduler makes every usleep() take at least
 	// 20ms, so we need a long time to ensure all goroutines have
 	// run. If they haven't run after 30ms, give it another 1000ms
 	// and check again.
 	time.Sleep(30 * time.Millisecond)
 	var fail bool
 	for i := range count {
 		if atomic.LoadInt64(&count[i]) == 0 {
 			fail = true
 		}
 	}
 	if fail {
 		time.Sleep(1 * time.Second)
 		for i := range count {
 			if atomic.LoadInt64(&count[i]) == 0 {
 				fmt.Printf("goroutine %d did not run\n", i)
 				return
 			}
 		}
 	}
 	fmt.Println("OK")
 }

 func GCPhys() {
 	// This test ensures that heap-growth scavenging is working as intended.
 	//
 	// It sets up a specific scenario: it allocates two pairs of objects whose
 	// sizes sum to size. One object in each pair is "small" (though must be
 	// large enough to be considered a large object by the runtime) and one is
 	// large. The small objects are kept while the large objects are freed,
 	// creating two large unscavenged holes in the heap. The heap goal should
 	// also be small as a result (so size must be at least as large as the
 	// minimum heap size). We then allocate one large object, bigger than both
 	// pairs of objects combined. This allocation, because it will tip
 	// HeapSys-HeapReleased well above the heap goal, should trigger heap-growth
 	// scavenging and scavenge most, if not all, of the large holes we created
 	// earlier.
 	const (
 		// Size must be also large enough to be considered a large
 		// object (not in any size-segregated span).
 		size    = 4 << 20
 		split   = 64 << 10
 		objects = 2

 		// The page cache could hide 64 8-KiB pages from the scavenger today.
 		maxPageCache = (8 << 10) * 64

 		// Reduce GOMAXPROCS down to 4 if it's greater. We need to bound the amount
 		// of memory held in the page cache because the scavenger can't reach it.
 		// The page cache will hold at most maxPageCache of memory per-P, so this
 		// bounds the amount of memory hidden from the scavenger to 4*maxPageCache
 		// at most.
 		maxProcs = 4
 	)
 	// Set GOGC so that this test operates under consistent assumptions.
 	debug.SetGCPercent(100)
 	procs := runtime.GOMAXPROCS(-1)
 	if procs > maxProcs {
 		defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(maxProcs))
 		procs = runtime.GOMAXPROCS(-1)
 	}
 	// Save objects which we want to survive, and condemn objects which we don't.
 	// Note that we condemn objects in this way and release them all at once in
 	// order to avoid having the GC start freeing up these objects while the loop
 	// is still running and filling in the holes we intend to make.
 	saved := make([][]byte, 0, objects+1)
 	condemned := make([][]byte, 0, objects)
 	for i := 0; i < 2*objects; i++ {
 		if i%2 == 0 {
 			saved = append(saved, make([]byte, split))
 		} else {
 			condemned = append(condemned, make([]byte, size-split))
 		}
 	}
 	condemned = nil
 	// Clean up the heap. This will free up every other object created above
 	// (i.e. everything in condemned) creating holes in the heap.
 	// Also, if the condemned objects are still being swept, its possible that
 	// the scavenging that happens as a result of the next allocation won't see
 	// the holes at all. We call runtime.GC() twice here so that when we allocate
 	// our large object there's no race with sweeping.
 	runtime.GC()
 	runtime.GC()
 	// Perform one big allocation which should also scavenge any holes.
 	//
 	// The heap goal will rise after this object is allocated, so it's very
 	// important that we try to do all the scavenging in a single allocation
 	// that exceeds the heap goal. Otherwise the rising heap goal could foil our
 	// test.
 	saved = append(saved, make([]byte, objects*size))
 	// Clean up the heap again just to put it in a known state.
 	runtime.GC()
 	// heapBacked is an estimate of the amount of physical memory used by
 	// this test. HeapSys is an estimate of the size of the mapped virtual
 	// address space (which may or may not be backed by physical pages)
 	// whereas HeapReleased is an estimate of the amount of bytes returned
 	// to the OS. Their difference then roughly corresponds to the amount
 	// of virtual address space that is backed by physical pages.
 	var stats runtime.MemStats
 	runtime.ReadMemStats(&stats)
 	heapBacked := stats.HeapSys - stats.HeapReleased
 	// If heapBacked does not exceed the heap goal by more than retainExtraPercent
 	// then the scavenger is working as expected; the newly-created holes have been
 	// scavenged immediately as part of the allocations which cannot fit in the holes.
 	//
 	// Since the runtime should scavenge the entirety of the remaining holes,
 	// theoretically there should be no more free and unscavenged memory. However due
 	// to other allocations that happen during this test we may still see some physical
 	// memory over-use.
 	overuse := (float64(heapBacked) - float64(stats.HeapAlloc)) / float64(stats.HeapAlloc)
 	// Compute the threshold.
 	//
 	// In theory, this threshold should just be zero, but that's not possible in practice.
 	// Firstly, the runtime's page cache can hide up to maxPageCache of free memory from the
 	// scavenger per P. To account for this, we increase the threshold by the ratio between the
 	// total amount the runtime could hide from the scavenger to the amount of memory we expect
 	// to be able to scavenge here, which is (size-split)*objects. This computation is the crux
 	// GOMAXPROCS above; if GOMAXPROCS is too high the threshold just becomes 100%+ since the
 	// amount of memory being allocated is fixed. Then we add 5% to account for noise, such as
 	// other allocations this test may have performed that we don't explicitly account for The
 	// baseline threshold here is around 11% for GOMAXPROCS=1, capping out at around 30% for
 	// GOMAXPROCS=4.
 	threshold := 0.05 + float64(procs)*maxPageCache/float64((size-split)*objects)
 	if overuse <= threshold {
 		fmt.Println("OK")
 		return
 	}
 	// Physical memory utilization exceeds the threshold, so heap-growth scavenging
 	// did not operate as expected.
 	//
 	// In the context of this test, this indicates a large amount of
 	// fragmentation with physical pages that are otherwise unused but not
 	// returned to the OS.
 	fmt.Printf("exceeded physical memory overuse threshold of %3.2f%%: %3.2f%%\n"+
 		"(alloc: %d, goal: %d, sys: %d, rel: %d, objs: %d)\n", threshold*100, overuse*100,
 		stats.HeapAlloc, stats.NextGC, stats.HeapSys, stats.HeapReleased, len(saved))
 	runtime.KeepAlive(saved)
 }

 // Test that defer closure is correctly scanned when the stack is scanned.
 func DeferLiveness() {
 	var x [10]int
 	escape(&x)
 	fn := func() {
 		if x[0] != 42 {
 			panic("FAIL")
 		}
 	}
 	defer fn()

 	x[0] = 42
 	runtime.GC()
 	runtime.GC()
 	runtime.GC()
 }

 //go:noinline
 func escape(x interface{}) { sink2 = x; sink2 = nil }

 var sink2 interface{}
	// Copyright 2015 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package main

	import (
	"fmt"
	"os"
	"runtime"
	"runtime/debug"
	"sync/atomic"
	"time"
	)

	func init() {
	register("GCFairness", GCFairness)
	register("GCFairness2", GCFairness2)
	register("GCSys", GCSys)
	register("GCPhys", GCPhys)
	register("DeferLiveness", DeferLiveness)
	}

	func GCSys() {
	runtime.GOMAXPROCS(1)
	memstats := new(runtime.MemStats)
	runtime.GC()
	runtime.ReadMemStats(memstats)
	sys := memstats.Sys

	runtime.MemProfileRate = 0 // disable profiler

	itercount := 100000
	for i := 0; i < itercount; i++ {
	workthegc()
	}

	// Should only be using a few MB.
	// We allocated 100 MB or (if not short) 1 GB.
	runtime.ReadMemStats(memstats)
	if sys > memstats.Sys {
	sys = 0
	} else {
	sys = memstats.Sys - sys
	}
	if sys > 16<<20 {
	fmt.Printf("using too much memory: %d bytes\n", sys)
	return
	}
	fmt.Printf("OK\n")
	}

	var sink []byte

	func workthegc() []byte {
	sink = make([]byte, 1029)
	return sink
	}

	func GCFairness() {
	runtime.GOMAXPROCS(1)
	f, err := os.Open("/dev/null")
	if os.IsNotExist(err) {
	// This test tests what it is intended to test only if writes are fast.
	// If there is no /dev/null, we just don't execute the test.
	fmt.Println("OK")
	return
	}
	if err != nil {
	fmt.Println(err)
	os.Exit(1)
	}
	for i := 0; i < 2; i++ {
	go func() {
	for {
	f.Write([]byte("."))
	}
	}()
	}
	time.Sleep(10 * time.Millisecond)
	fmt.Println("OK")
	}

	func GCFairness2() {
	// Make sure user code can't exploit the GC's high priority
	// scheduling to make scheduling of user code unfair. See
	// issue #15706.
	runtime.GOMAXPROCS(1)
	debug.SetGCPercent(1)
	var count [3]int64
	var sink [3]interface{}
	for i := range count {
	go func(i int) {
	for {
	sink[i] = make([]byte, 1024)
	atomic.AddInt64(&count[i], 1)
	}
	}(i)
	}
	// Note: If the unfairness is really bad, it may not even get
	// past the sleep.
	//
	// If the scheduling rules change, this may not be enough time
	// to let all goroutines run, but for now we cycle through
	// them rapidly.
	//
	// OpenBSD's scheduler makes every usleep() take at least
	// 20ms, so we need a long time to ensure all goroutines have
	// run. If they haven't run after 30ms, give it another 1000ms
	// and check again.
	time.Sleep(30 * time.Millisecond)
	var fail bool
	for i := range count {
	if atomic.LoadInt64(&count[i]) == 0 {
	fail = true
	}
	}
	if fail {
	time.Sleep(1 * time.Second)
	for i := range count {
	if atomic.LoadInt64(&count[i]) == 0 {
	fmt.Printf("goroutine %d did not run\n", i)
	return
	}
	}
	}
	fmt.Println("OK")
	}

	func GCPhys() {
	// This test ensures that heap-growth scavenging is working as intended.
	//
	// It sets up a specific scenario: it allocates two pairs of objects whose
	// sizes sum to size. One object in each pair is "small" (though must be
	// large enough to be considered a large object by the runtime) and one is
	// large. The small objects are kept while the large objects are freed,
	// creating two large unscavenged holes in the heap. The heap goal should
	// also be small as a result (so size must be at least as large as the
	// minimum heap size). We then allocate one large object, bigger than both
	// pairs of objects combined. This allocation, because it will tip
	// HeapSys-HeapReleased well above the heap goal, should trigger heap-growth
	// scavenging and scavenge most, if not all, of the large holes we created
	// earlier.
	const (
	// Size must be also large enough to be considered a large
	// object (not in any size-segregated span).
	size = 4 << 20
	split = 64 << 10
	objects = 2

	// The page cache could hide 64 8-KiB pages from the scavenger today.
	maxPageCache = (8 << 10) * 64

	// Reduce GOMAXPROCS down to 4 if it's greater. We need to bound the amount
	// of memory held in the page cache because the scavenger can't reach it.
	// The page cache will hold at most maxPageCache of memory per-P, so this
	// bounds the amount of memory hidden from the scavenger to 4*maxPageCache
	// at most.
	maxProcs = 4
	)
	// Set GOGC so that this test operates under consistent assumptions.
	debug.SetGCPercent(100)
	procs := runtime.GOMAXPROCS(-1)
	if procs > maxProcs {
	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(maxProcs))
	procs = runtime.GOMAXPROCS(-1)
	}
	// Save objects which we want to survive, and condemn objects which we don't.
	// Note that we condemn objects in this way and release them all at once in
	// order to avoid having the GC start freeing up these objects while the loop
	// is still running and filling in the holes we intend to make.
	saved := make([][]byte, 0, objects+1)
	condemned := make([][]byte, 0, objects)
	for i := 0; i < 2*objects; i++ {
	if i%2 == 0 {
	saved = append(saved, make([]byte, split))
	} else {
	condemned = append(condemned, make([]byte, size-split))
	}
	}
	condemned = nil
	// Clean up the heap. This will free up every other object created above
	// (i.e. everything in condemned) creating holes in the heap.
	// Also, if the condemned objects are still being swept, its possible that
	// the scavenging that happens as a result of the next allocation won't see
	// the holes at all. We call runtime.GC() twice here so that when we allocate
	// our large object there's no race with sweeping.
	runtime.GC()
	runtime.GC()
	// Perform one big allocation which should also scavenge any holes.
	//
	// The heap goal will rise after this object is allocated, so it's very
	// important that we try to do all the scavenging in a single allocation
	// that exceeds the heap goal. Otherwise the rising heap goal could foil our
	// test.
	saved = append(saved, make([]byte, objects*size))
	// Clean up the heap again just to put it in a known state.
	runtime.GC()
	// heapBacked is an estimate of the amount of physical memory used by
	// this test. HeapSys is an estimate of the size of the mapped virtual
	// address space (which may or may not be backed by physical pages)
	// whereas HeapReleased is an estimate of the amount of bytes returned
	// to the OS. Their difference then roughly corresponds to the amount
	// of virtual address space that is backed by physical pages.
	var stats runtime.MemStats
	runtime.ReadMemStats(&stats)
	heapBacked := stats.HeapSys - stats.HeapReleased
	// If heapBacked does not exceed the heap goal by more than retainExtraPercent
	// then the scavenger is working as expected; the newly-created holes have been
	// scavenged immediately as part of the allocations which cannot fit in the holes.
	//
	// Since the runtime should scavenge the entirety of the remaining holes,
	// theoretically there should be no more free and unscavenged memory. However due
	// to other allocations that happen during this test we may still see some physical
	// memory over-use.
	overuse := (float64(heapBacked) - float64(stats.HeapAlloc)) / float64(stats.HeapAlloc)
	// Compute the threshold.
	//
	// In theory, this threshold should just be zero, but that's not possible in practice.
	// Firstly, the runtime's page cache can hide up to maxPageCache of free memory from the
	// scavenger per P. To account for this, we increase the threshold by the ratio between the
	// total amount the runtime could hide from the scavenger to the amount of memory we expect
	// to be able to scavenge here, which is (size-split)*objects. This computation is the crux
	// GOMAXPROCS above; if GOMAXPROCS is too high the threshold just becomes 100%+ since the
	// amount of memory being allocated is fixed. Then we add 5% to account for noise, such as
	// other allocations this test may have performed that we don't explicitly account for The
	// baseline threshold here is around 11% for GOMAXPROCS=1, capping out at around 30% for
	// GOMAXPROCS=4.
	threshold := 0.05 + float64(procs)maxPageCache/float64((size-split)objects)
	if overuse <= threshold {
	fmt.Println("OK")
	return
	}
	// Physical memory utilization exceeds the threshold, so heap-growth scavenging
	// did not operate as expected.
	//
	// In the context of this test, this indicates a large amount of
	// fragmentation with physical pages that are otherwise unused but not
	// returned to the OS.
	fmt.Printf("exceeded physical memory overuse threshold of %3.2f%%: %3.2f%%\n"+
	"(alloc: %d, goal: %d, sys: %d, rel: %d, objs: %d)\n", threshold100, overuse100,
	stats.HeapAlloc, stats.NextGC, stats.HeapSys, stats.HeapReleased, len(saved))
	runtime.KeepAlive(saved)
	}

	// Test that defer closure is correctly scanned when the stack is scanned.
	func DeferLiveness() {
	var x [10]int
	escape(&x)
	fn := func() {
	if x[0] != 42 {
	panic("FAIL")
	}
	}
	defer fn()

	x[0] = 42
	runtime.GC()
	runtime.GC()
	runtime.GC()
	}

	//go:noinline
	func escape(x interface{}) { sink2 = x; sink2 = nil }

	var sink2 interface{}